The act in which one cosumes alchohol prior to attending an event at which alcholic beverages may or may not be served. Often popular with university or college students who can't afford to buy to many drinks at a bar or high school kids who plan to attend events such as dances.

Are you going to Paddy Connolly's tonite? Yea but we are going to pre-drink at Dave's.

Before Johnny went to the dance he pre-drank a mickey at Paul's house.

Sometimes shortened to pre. A small party usually held in someone's house where people drink store bought alcohol before going out to a bar or club. This usually means they are tipsy or nearly drunk by the time they arrive, meaning they do not have to buy expensive drinks at the bar

Joe - "Are you going out tonight?"
Jason - "Yeah, Emma's parents are out of town so she's having predrinks at hers"
Joe - "Count me in"